Pulmonary injury following exposure to amorphous silicon dioxide nanoparticles in Golden Syrian Hamsters

Amorphous silicon dioxide nanoparticles (SiO₂ NPs) are abundant within the earth's crust and can be released into the air through industrial and manufacturing activities. Such materials are often used in industrial processes, in pharmaceutical and in the cosmetic industries. Amorphous SiO₂ NPs are pulmonary toxicants; however, the mechanism of toxicity is uncertain. In the current study, toxicity of SiO₂ NPs was assessed using inhalation exposure in an in vivo system to study a possible mechanism of pulmonary injury. Golden Syrian Hamsters were divided into 4 groups: 1- room air control, 2- vehicle control, 3- low concentration (6 mg/m³) and 4- high concentration (12 mg/m³). Hamsters were treated for 4 h a day for 8 days. Bronchoalveolar Lavage Fluid (BALF) analysis found increases in total cell counts (p < 0.0001), neutrophils (p < 0.0001), lymphocytes (p < 0.001), eosinophils (p < 0.01), multinucleated macrophages (p < 0.01), total protein (p < 0.0001), alkaline phosphatase (p < 0.0001), and lactate dehydrogenase (p < 0.001) in the high concentration group. Histopathological analysis found an increase in air space, quantified by Mean Linear Intercept (p < 0.0001), and a significant increase in TUNEL positive cells (p < 0.001), in the high concentration group. SEM and TEM found structural alterations to the lung tissue including increase in the number holes in the alveolar walls and in apoptotic bodies within tissue. Caspase 3 (p < 0.05), and 8 (p < 0.05), were significantly increased along with cellular inflammation markers TNF-α (p < 0.05), and HSP70 (p < 0.05) in the high concentration group. Results of the study indicate exposure to SiO₂ NPs may induce extrinsic apoptotic pathway, leading to tissue damage and significant airspace enlargement.